Kusasalethu is situated in the West Wits Basin with the Ventersdorp Contact Reef being mined as the main orebody.

Kusasalethu’s Ventersdorp Contact Reef facies model is based on the paleotopographic or slope and terrace model. Nine facies types have been identified – eight sedimentological and one structural. Four of the facies are thick, high-grade, geologically distinct reef terraces, separated from one another by a thin low-grade slope reef. The sand-filled channel is a thick, low-grade facies.

The Sandy Terrace Complex is found on the same elevation as the Terrace Complex but is essentially a pebbly quartzite with no grade. The Mondeor conglomerates have been identified sub-cropping against the Ventersdorp Contact Reef in stopes in certain areas and have been delineated as separate facies in these areas.

The Elsburg conglomerates, found on the western side of Kusasalethu, form the footwall to the Ventersdorp Contact Reef and are part of the Turffontein Supergroup. It is a predominantly polymictic matrixsupported conglomerate of well-packed and moderately sorted, subrounded smoky (80%), black-grey (15%) quartz pebbles, chert (3%) and some elongated shale pebbles (2%). The matrix is pale yellow to light green and medium-grained and pyritic in places.

The Ventersdorp Contact Reef is overlain by the Ventersdorp Lava belonging to the Ventersdorp Supergroup. The reef is light to mid-grey in colour and fine crystalline, seldom containing phenocrysts. In places it is amygdaloidal with quartz and pyrite mineralisation. Flow structures are also present at the base of the lava. It breaks into very angular fragments due to weak jointing and flow banding – it would appear to be andesitic in composition.

Geological discontinuities observed at Kusasalethu include faults, dykes and sills. Sills may occur in the footwall, in areas adjacent to certain dykes. Flat bedding plane faulting also occurs and results in reef duplication, elimination and brecciation. Faults and dykes are classified according to their relative geologic ages as follows: PreVentersdorp Contact Reef, or Ventersdorp, Platberg, Bushveld or Pilanesberg structures.

Kusasalethu mines in blocky ground created by structures in the form of dykes and faults. The dykes are fairly basic in composition and tend to strike north-north-east and south-south-west with a general dip of 75 degrees. The faults, however, have a strike mostly of east-southeast and west- north-west with a few exceptions. Generally, these are normal faults with the accompanying loss of ground with varying throws – from mere centimetres to a massive 60m (the Kittims and De Twem faults).

The mine comprises twin vertical and twin sub-vertical shaft systems, and uses conventional mining methods in a sequential grid layout. Mining is conducted to a depth of 3 388m and is Harmony’s deepest mine.

The 10m-diameter rock/ventilation shaft was initially sunk to 2 195m and the man/material shaft to 2 127m. By June 1984, a 10m-diameter sub-vertical rock/service shaft had been completed to a depth of 3 048m and a 7m-diameter sub-vertical ventilation shaft to a depth of 3 048m. Both shafts were deepened to a final depth below surface of 3 318m and 3 388m respectively as part of the deepening project to extract the higher-grade pay shoot towards the west of the mine. In December 2014, a decision was taken to suspend operations in the old portion of Kusasalethu and to restructure the mine. Subsequently, mining above 98 level ceased.

Mining is by means of sequential grids with regional dip stabilising pillars, backfill and pre-conditioning to offset the effects of mining at this depth. Mining is conducted over five levels from 98 level to 113 level. Large geological structures are stabilised by means of clamping pillars.

The Harmony Kusasalethu Gold Plant is situated 18 km from Carletonville, Gauteng, South Africa.

Ore Reception Run of Mine (ROM) is conveyed from underground to the stock pile facility of 28 000 tons capacity. The stock pile material feeds to the three parallel silo bins of 2550 tons live storage capacity, from which ore is drawn from each silo to be taken to the three parallel run of mine mills for grinding to required size. Steel balls are used as grinding media, supplemented by wide range particle size of mill feed. There is a two stage classification for each mill with each primary cyclone overflow combined into a common tank, the secondary cyclone feed tank, for second stage classification by secondary cyclone. The overflow of the secondary cyclone is further screened on a linear screen for the removal of coarse woodchips and tramp steel.

Ore mined is processed on site at the Kusasalethu gold plant. Gold is extracted by means of milling, cyanide leaching, carbon-in-pulp concentration and electrowinning to absorb the carbon to produce doré. No smelting is done on site and the gold doré is dispatched to Rand Refinery.

There are three thickeners, two of which are always online, fed from a distribution box of the thickeners feed launder, with the one thickener available as a standby in case of emergency. Calcium oxide (lime) is added at the thickeners for maintaining a level of alkalinity. Flocculant is added to aid with settling of solids. The overflow water of the thickeners gravitates to the two mill return tanks to be reused in the milling process.

The leach circuit consist of 12 tanks, cyanide is automatically added to Leach tank 9 at a concentration necessary for the dissolution of gold. Compressed air is used to agitate the slurry, suspending solids in pulp and raising dissolved oxygen.